Caesar Cipher
Encode and decode text with the classic Caesar cipher by shifting each letter a fixed number of places, or brute-force all 26 shifts to crack a message with an unknown key. Free, instant and fully private in your browser.
All 26 possible shifts
Each row shifts your text by that amount. When decoding an unknown message, look for the row that reads as plain English.
| Shift | Result |
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How to use the Caesar cipher tool
- Enter your text. Type or paste the message you want to encode or decode into the text box.
- Set the mode and shift. Choose Encode or Decode and drag the slider to pick a shift from 0 to 25. The result updates instantly.
- Cracking an unknown key? Press Brute-force all shifts to see every one of the 26 possible outputs at once and spot the readable one.
About this tool
The Caesar cipher is one of the oldest known encryption methods, named after Julius Caesar, who reportedly used it to protect military messages. It works by shifting every letter of the alphabet a fixed number of positions: with a shift of 3, A becomes D, B becomes E, and so on, wrapping around from Z back to A. Decoding simply shifts each letter back by the same amount. Letters keep their original case, and digits, spaces and punctuation are left untouched.
Because there are only 25 usable shifts, the Caesar cipher offers no real security today and can be broken in seconds — which is exactly why the built-in brute-force view lists all 26 outputs for you. It remains a favourite for teaching the basics of cryptography, for puzzles and escape rooms, and for the ROT13 variant used to hide spoilers. Everything is processed locally in your browser, so your text is never uploaded or stored.
Frequently asked questions
What shift value should I use?
Any number from 1 to 25 works. A shift of 3 is the classic value used by Julius Caesar, and a shift of 13 produces ROT13, which is its own inverse. A shift of 0 leaves the text unchanged.
How do I decode a message when I do not know the shift?
Use the Brute-force all shifts button. It applies every possible shift and shows all 26 results, so you can scan the list and pick the one that turns into readable text.
Does it change numbers, spaces or punctuation?
No. Only the 26 letters A–Z are shifted. Digits, spaces, symbols and line breaks pass through unchanged, and the upper- or lower-case of each letter is preserved.
Is the Caesar cipher secure?
Not at all by modern standards — with only 25 possible keys it can be cracked instantly by trying them all. It is great for learning and for fun, but never use it to protect anything that actually needs to stay secret.